Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: add verifier tests for wide stores

From: Stanislav Fomichev <[email-masked]>
Date: Mon, 1 Jul 2019 09:00:45 -0700

On 06/30, Yonghong Song wrote:
> 
> 
> On 6/28/19 4:10 PM, Stanislav Fomichev wrote:
> > Make sure that wide stores are allowed at proper (aligned) addresses.
> > Note that user_ip6 is naturally aligned on 8-byte boundary, so
> > correct addresses are user_ip6[0] and user_ip6[2]. msg_src_ip6 is,
> > however, aligned on a 4-byte bondary, so only msg_src_ip6[1]
> > can be wide-stored.
> > 
> > Cc: Andrii Nakryiko <[email-masked]>
> > Cc: Yonghong Song <[email-masked]>
> > Signed-off-by: Stanislav Fomichev <[email-masked]>
> > ---
> >   tools/testing/selftests/bpf/test_verifier.c   | 17 ++++++--
> >   .../selftests/bpf/verifier/wide_store.c       | 40 +++++++++++++++++++
> >   2 files changed, 54 insertions(+), 3 deletions(-)
> >   create mode 100644 tools/testing/selftests/bpf/verifier/wide_store.c
> > 
> > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > index c5514daf8865..b0773291012a 100644
> > --- a/tools/testing/selftests/bpf/test_verifier.c
> > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > @@ -105,6 +105,7 @@ struct bpf_test {
> >   			__u64 data64[TEST_DATA_LEN / 8];
> >   		};
> >   	} retvals[MAX_TEST_RUNS];
> > +	enum bpf_attach_type expected_attach_type;
> >   };
> >   
> >   /* Note we want this to be 64 bit aligned so that the end of our array is
> > @@ -850,6 +851,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
> >   	int fd_prog, expected_ret, alignment_prevented_execution;
> >   	int prog_len, prog_type = test->prog_type;
> >   	struct bpf_insn *prog = test->insns;
> > +	struct bpf_load_program_attr attr;
> >   	int run_errs, run_successes;
> >   	int map_fds[MAX_NR_MAPS];
> >   	const char *expected_err;
> > @@ -881,8 +883,17 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
> >   		pflags |= BPF_F_STRICT_ALIGNMENT;
> >   	if (test->flags & F_NEEDS_EFFICIENT_UNALIGNED_ACCESS)
> >   		pflags |= BPF_F_ANY_ALIGNMENT;
> > -	fd_prog = bpf_verify_program(prog_type, prog, prog_len, pflags,
> > -				     "GPL", 0, bpf_vlog, sizeof(bpf_vlog), 4);
> > +
> > +	memset(&attr, 0, sizeof(attr));
> > +	attr.prog_type = prog_type;
> > +	attr.expected_attach_type = test->expected_attach_type;
> > +	attr.insns = prog;
> > +	attr.insns_cnt = prog_len;
> > +	attr.license = "GPL";
> > +	attr.log_level = 4;
> > +	attr.prog_flags = pflags;
> > +
> > +	fd_prog = bpf_load_program_xattr(&attr, bpf_vlog, sizeof(bpf_vlog));
> >   	if (fd_prog < 0 && !bpf_probe_prog_type(prog_type, 0)) {
> >   		printf("SKIP (unsupported program type %d)\n", prog_type);
> >   		skips++;
> > @@ -912,7 +923,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
> >   			printf("FAIL\nUnexpected success to load!\n");
> >   			goto fail_log;
> >   		}
> > -		if (!strstr(bpf_vlog, expected_err)) {
> > +		if (!expected_err || !strstr(bpf_vlog, expected_err)) {
> >   			printf("FAIL\nUnexpected error message!\n\tEXP: %s\n\tRES: %s\n",
> >   			      expected_err, bpf_vlog);
> >   			goto fail_log;
> > diff --git a/tools/testing/selftests/bpf/verifier/wide_store.c b/tools/testing/selftests/bpf/verifier/wide_store.c
> > new file mode 100644
> > index 000000000000..c6385f45b114
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/verifier/wide_store.c
> > @@ -0,0 +1,40 @@
> > +#define BPF_SOCK_ADDR(field, off, res, err) \
> > +{ \
> > +	"wide store to bpf_sock_addr." #field "[" #off "]", \
> > +	.insns = { \
> > +	BPF_MOV64_IMM(BPF_REG_0, 1), \
> > +	BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, \
> > +		    offsetof(struct bpf_sock_addr, field[off])), \
> > +	BPF_EXIT_INSN(), \
> > +	}, \
> > +	.result = res, \
> > +	.prog_type = BPF_PROG_TYPE_CGROUP_SOCK_ADDR, \
> > +	.expected_attach_type = BPF_CGROUP_UDP6_SENDMSG, \
> > +	.errstr = err, \
> > +}
> > +
> > +/* user_ip6[0] is u64 aligned */
> > +BPF_SOCK_ADDR(user_ip6, 0, ACCEPT,
> > +	      NULL),
> > +BPF_SOCK_ADDR(user_ip6, 1, REJECT,
> > +	      "invalid bpf_context access off=12 size=8"),
> > +BPF_SOCK_ADDR(user_ip6, 2, ACCEPT,
> > +	      NULL),
> > +BPF_SOCK_ADDR(user_ip6, 3, REJECT,
> > +	      "invalid bpf_context access off=20 size=8"),
> > +BPF_SOCK_ADDR(user_ip6, 4, REJECT,
> > +	      "invalid bpf_context access off=24 size=8"),
> 
> With offset 4, we have
> #968/p wide store to bpf_sock_addr.user_ip6[4] OK
> 
> This test case can be removed. user code typically
> won't write bpf_sock_addr.user_ip6[4], and compiler
> typically will give a warning since it is out of
> array bound. Any particular reason you want to
> include this one?
Agreed on both, I'm being overly cautious here. They should
be caught by the outer switch and be rejected because of
other reasons.

> > +
> > +/* msg_src_ip6[0] is _not_ u64 aligned */
> > +BPF_SOCK_ADDR(msg_src_ip6, 0, REJECT,
> > +	      "invalid bpf_context access off=44 size=8"),
> > +BPF_SOCK_ADDR(msg_src_ip6, 1, ACCEPT,
> > +	      NULL),
> > +BPF_SOCK_ADDR(msg_src_ip6, 2, REJECT,
> > +	      "invalid bpf_context access off=52 size=8"),
> > +BPF_SOCK_ADDR(msg_src_ip6, 3, REJECT,
> > +	      "invalid bpf_context access off=56 size=8"),
> > +BPF_SOCK_ADDR(msg_src_ip6, 4, REJECT,
> > +	      "invalid bpf_context access off=60 size=8"),
> 
> The same as above, offset=4 case can be removed?
> 
> > +
> > +#undef BPF_SOCK_ADDR
> >